The use of hydrogen and other gaseous fuels for vehicles is not new. For example, compressed natural gas (CNG) has occasionally been used as the fuel for internal combustion powered fleet vehicles in markets where CNG represented a low cost, low emission, and relatively high octane fuel source.
The allure of hydrogen as a fuel flows the most basic of chemical formulae: hydrogen plus oxygen equals water. This formula suggests that many of our vehicle related air quality problems could be eliminated simply by fueling future vehicles with hydrogen gas whether they are powered by conventional internal combustion engines, fuel cells, or hybrid fuel cell battery systems.
In general, however, a major problem with gaseous fuels has always been how and where to store such fuel in a vehicle. All gaseous fuel must be compressed to some degree to increase its energy density. Compression by itself requires the use of a reinforced storage tank. Unfortunately, even very high compression does not drastically reduce gaseous fuel volume and a relatively large tank is required if the average vehicle is to have a reasonable driving range between fuel fills. Thus, using gaseous fuel on a vehicle requires using a relatively large, reinforced tank.
In the past, the use of gaseous fuels has typically been limited to larger vehicles, such as trucks, due in part to the relatively large size of the fuel tanks necessary to provide fuel to power the vehicle over an acceptable range. Such tanks are described in U.S. Pat. No. 5,810,309 (mounting assembly for retrofitting a CNG tank to an existing vehicle by cutting part of the frame); U.S. Pat. No. 6,042,071 (mounting assembly for a large CNG tank that takes over the trunk compartment and accommodates expansion and contraction of the tank); and U.S. Pat. No. 6,536,722 (rack for mounting a number of CNG tanks such as on a bus).
Hybrid vehicles that combine gaseous fueled engines or fuel cells with batteries and electric motors are currently under development. These hybrids are designed with a hydrogen tank in the trunk similar to that described in U.S. Pat. No. 6,536,722.
Current tank designs for compressed gaseous fuel have a number of drawbacks. For example, gaseous fuel tanks are almost too large to be used in compact vehicles. In mid to full size passenger cars, gaseous fuel tanks require almost all the space in the trunk. In small trucks, part of the cargo area must be used to accommodate a gaseous fuel tank. The problem of accommodating a compressed gas tank is exacerbated in a hybrid vehicle where available storage space is frequently limited by the other systems present.